Insulation embedded ballast unit



1951 T. s. BJORKLUND INSULATION EMBEDDED BALLAST UNIT Filed Feb. 27,1948 INVENTOR TORE SIGVARD BJaRKLUND ATTORNEYS Patented Oct. 23, 1951INSULATION EMBEDDED BALLAST UNIT Tore SigvardBj'iirklund, Stockholm,Sweden, as-

signor to Lumalampan Aktiebolag, Stockholm, Sweden, a corporation ofSweden- Application February 27, 1948, Serial No. 11,528 In SwedenDecember 30, 1946 1 Claim. 1

This invention relates to a series impedance in the form of a choke ortransformer for electric discharge tubes for illuminating purposes, asfor instance light tubes.

A common series impedance for light tubes and similar illuminating tubesconsists of an iron core composed of laminae and of suitable choke ortransformer windings arranged on the core. Over the unit composed inthis manner in all cases known in practice a casing is fitted, by meansof which the impedance is installed in the mounting. The vibrations inthe laminae cause during operation disturbing sounds, which furthermorecan be amplified by the influence of the casing. In some instances theiron core has therefore been cast with its windings into a massive lumpof some asphalt composition, but a special outer protective casing isstill used for installing the impedance electrically as well asmechanically in the mounting.

Now this invention relates to a special design of a choke or transformercast into an insulating mass. The impedance referred to is characterizedby the feature that its winding and iron core composed of laminae arecast without previous vacuum impregnation of the windings into anenvelope, consisting of a hardenable synthetic mass and entirelyembedding the above mentioned parts. This envelope has the exteriorshape of a choke or transformer casing and is fitted with screw holesand other fastening devices and with cast-in connections forinstallation of the impedance. furthermore mutually united to a packsolely by their being baked into the synthetic mass.

In a special design of the series impedance according to the invention,longitudinal slots are pressed into its underside for the insertion ofwires. These slots may suitably be provided with end walls which can bebroken away. The impedance can thus be placed on a flat surface and betraversed by wires.

An impedance designed in accordance with the invention is shown inenclosed drawing. It consists of an iron core composed of laminae I inthe shape of a rectangular frame with a 1ongitudinal leg 6. The core airgaps are numbered 5 and II. On the leg are slipped two winding coils 3and l, which are shown provided with end supports of pressboard or someother suitable insulating material. The iron core l and the windings 3and I are entirely cast into an envelope l2 of a hardenable syntheticmass such as phenol formaldehyde resins. For producing the envelope theiron core with the windings The core laminae are surrounded by pulveroussynthetic mass is placed in a press mould arranged for being heated. Apress-stamp is dropped and compresses the synthetic mass to form anenvelope [2 of such exterior shape that the envelope of synthetic massserves direct as a casing and consequently an extra protective casing isno longer necessary. The thickness of the envelope can at most points bemade about 2 mm. Its upper side is provided with a shoulder 2, thesurface of which has been made plane for the greater part to permitstamping in of the impedance marking. For this reason the wall thicknessof the envelope there exceeds the thickness by about 2 mm. at somepoints and therefore does not entirely follow the contour of thebaked-in material. The ends of the laminae are provided with holes,through which a. mandrel is inserted during the bakingin process. Inthis way two screw holes 8 and I! are obtained for installation of theimpedance in its mounting position. The windings 3 and l have sturdilysleeved wire ends 9, l0, l4 and I6 for electrical connection of theimpedance. These sleeved ends are also baked in at their inner ends sothat they are securely fixed in the hardened mass, which was originatedwhen pressing the cover. On the underside of the cover longitudinalslots [3 and I5 have been pressed in when the cover was made. They areintended for hiding such connecting wires, which must be drawn past theimpedance in connection With installation in mounting position. Theseslots may be suitably limited by end walls which can be broken away,which gives the cover a closed appearance in cases, where such slots arenot utilized.

The casting of the cover under heavy pressure might be expected toexpose the windings, which consist of fine wire, to detrimental damage.This is, however, not the case, probably owing to the fact that thepressure is comparatively homogenously distributed. On account of thebaking-in process it will be seen that the hitherto usually employedvacuum impregnation of the impedance winding is no longer necessary. Thebolts and screws previously used for holding together the pack oflaminae can also be abolished, as it has become apparent that thelaminae are very effectively held together mutually when being bakedinto the synthetic mass.

What I claim is:

A ballast for electric discharge tubes for illuminating purposes,comprising a closed core structure consisting of a pile of iron laminaeplaced directly upon one another devoid of fastening means therefore andforming a frame having an air gap therein, an inductive unit positionedon a leg of said core structure, an envelope consisting of a bakedhardenable synthetic mass entirely embedding and surrounding said corestructure and said inductive unit and filling up said air gap, saidlaminae being mutually united to one another and to the pile solely bysaid baked synthetic mass, said ballast being provided with mechanicallyfastening and electrically connecting means anchored in the envelopemass and having longitudinal slots arranged in the underside of saidevelope for the insertion of Wires, and end Walls normally covering saidslots and limiting the length thereof, said walls being breakable 15 toexpose said slots.

TORE 'SIGVARD BJORKLUND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,132,297 Apple Mar. 16, 19151,326,366 Milton Dec. 30, 1919 1,427,324 Priestley Aug. 29, 19221,927,726 Hays Sept. 19, 1933 2,370,635 Bridges 1 Mar. 6, 1945 2,391,038Rifenbergh Dec. 18, 1945 2,423,869 Blessing July 15, 1947 2,484,215Foster Oct. 11, 1949

